- Age – Present from birth.
- Sex / gender – There is no difference in prevalence due to sex.
Syndromes associated with hypoplastic thumb include:
- VACTERL association – vertebral defects, anal atresia, cardiac defects, tracheoesophageal anomalies, and renal and limb anomalies
- Holt-Oram syndrome
- Fanconi anemia
- Thrombocytopenia with absent radius (TAR) syndrome
- CHARGE syndrome
Grade / classification system:
- Type I: Minor generalized hypoplasia.
- Type II: Absence of the intrinsic thenar muscles. First web space narrowing. Ulnar collateral ligament (UCL) insufficiency.
- Type III: Musculotendinous and osseous deficiencies.
- A – stable carpometacarpal (CMC) joint
- B – unstable CMC joint
- C – remnant head of metacarpal only
- Type IV: Pouce flottant, or floating thumb.
- Type V: Aplasia.